1. Field of the Invention
The present invention generally relates to refrigeration systems and, more particularly, relates to refrigeration systems including a plurality of evaporators and a compressor unit.
2. Related Art
In a typical refrigeration system, refrigerant circulates continuously through a closed circuit. The term "circuit", as used herein, refers to a physical apparatus whereas the term "cycle" as used herein refers to operation of a circuit, e.g., refrigerant cycles in a refrigeration circuit. The term "refrigerant", as used herein, refers to refrigerant in a liquid, vapor and/or gas form. Components of the closed circuit cause the refrigerant to undergo temperature/pressure changes. The temperature/pressure changes of the refrigerant result in energy transfer. Typical components of a refrigeration system include, for example, compressors, condensers, evaporators, control valve, and connecting piping. Details with regard to some known refrigeration systems are set forth in Baumeister et al., Standard Handbook for Mechanical Engineers, McGraw Hill Book Company, Eight Edition, 1979, beginning at page 19-6.
Energy efficiency is one important factor in the implementation of refrigeration systems. Particularly, an ideal refrigeration system provides an ideal refrigeration effect. In practice, an actual refrigeration system provides an actual refrigeration effect less than the ideal refrigeration effect. The actual refrigeration effect provided varies from system to system.
Increased energy efficiency typically is achieved by utilizing more expensive and more efficient refrigerant system components, adding extra insulation adjacent to the area to be refrigerated, or by other costly additions. Increasing the energy efficiency of a refrigeration system therefore usually results in an increase in the cost of the system. It is desirable, of course, to increase the efficiency of a refrigeration system and minimize any increase in the cost of the system.
In some apparatus utilizing refrigeration systems, more than one area is to be refrigerated, and at least one area requires more refrigeration than another area. A typical household refrigerator, which includes a freezer compartment and a fresh food compartment, is one example of such an apparatus. The freezer compartment preferably is maintained between -10.degree. Fahrenheit (F) and +15.degree. F., and the fresh food compartment preferably is maintained between +33.degree. F. and +47.degree. F.
To meet these temperature requirements, a typical refrigeration system includes a compressor coupled to an evaporator disposed within the household refrigerator. The terms "coupled" and "connected" are used herein interchangeably. When two components are coupled or connected, this means that the components are linked, directly or indirectly in some manner in refrigerant flow relationship. Another component or other components can be intervening between coupled or connected components. For example, even though other components such as a pressure sensor or an expander are connected or coupled in the link between the compressor and evaporator, the compressor and evaporator are still coupled or connected.
Referring again to the refrigeration system for a typical household refrigerator, the evaporator is operated so that it is maintained at approximately -10.degree. F. (an actual range of approximately -30.degree. F. to 0.degree. F. typically is used) and air is blown across the coils of the evaporator. The flow of the evaporator-cooled air is controlled, for example, by barriers. A first portion of the evaporator-cooled air is directed to the freezer compartment and a second portion of the evaporator-cooled air is directed to the fresh food compartment. To cool a fresh food compartment, rather than utilizing evaporator-cooled air from an evaporator operating at -10.degree. F., it is possible to utilize an evaporator operating at, for example, +25.degree. F. (or a range of approximately +15.degree. F. to +32.degree. F.) The typical refrigeration system utilized in household refrigerators, therefore, produces its refrigeration effect by operating an evaporator at a temperature which is appropriate for the freezer compartment but lower than it needs to be for the fresh food compartment.
It is well-known that the energy required to maintain an evaporator at -10 .degree. F. is greater than the energy required to maintain an evaporator at +25.degree. F. in a refrigerator. The typical household refrigerator therefore uses more energy to cool the fresh food compartment than is necessary. Using more energy than is necessary results in reduced energy efficiency.
The above referenced household refrigerator example is provided for illustrative purposes only. Many apparatus other than household refrigerators utilize refrigeration systems which include an evaporator operating at a temperature below a temperature at which the evaporator actually needs to operate.
Refrigeration systems which reduce energy use are described in commonly assigned U.S. Pat. Nos. 4,910,972 and 4,918,942. The patented systems utilize at least two evaporators and a plurality of compressors or a compressor having a plurality of stages. For example, in a dual, i.e., two, evaporator circuit for household refrigerators, a first evaporator operates at +25.degree. F. and a second evaporator operates at -10.degree. F. Air cooled by the first evaporator is utilized for the fresh food compartment and air cooled by the second evaporator is utilized for the freezer compartment. Utilizing the dual evaporator refrigeration system in a household refrigerator results in increased energy efficiency. Energy is conserved by operating the first evaporator at the temperature (e.g., +25.degree. F.) required for the fresh food compartment rather than operating an evaporator for the fresh food compartment at -10.degree. F. Other features of the patented systems also facilitate increased energy efficiencies.
To drive the plurality of evaporators in the refrigeration systems described in U.S. Pat. Nos. 4,910,972 and 4,918,942, and as mentioned above, a plurality of compressors or a compressor including a plurality of stages are utilized. Utilizing a plurality of compressors or utilizing a compressor having a plurality of stages results in increasing the cost of the refrigeration system over the cost, at least initially, of refrigeration systems utilizing one evaporator and one single stage compressor. It is desirable to provide improved energy efficiency achieved using a plurality of evaporators and to minimize, if not eliminate, the increase in cost associated with using a plurality of compressors or a compressor having a plurality of stages.
It is an object of the present invention to provide a refrigeration system which includes a single compressor unit coupled, directly or indirectly, to a plurality of evaporators.
Another object of the present invention is to provide a refrigeration system in which a single compressor unit alternately receives refrigerant flows having different, respective, pressures.
Yet another object of the present invention is to provide a refrigeration system which exhibits increased energy efficiency and minimizes any cost increases.
Still another object of the present invention is to provide a refrigeration system for a household refrigerator.